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use std::mem;
use std::ptr;
use std::slice;
pub struct PrefixedArray<I: PrefixedArrayInfo, T> {
inner: *mut Inner<I, T>,
}
pub trait PrefixedArrayInfo {
fn len(&self) -> usize;
fn capacity(&self) -> usize;
}
#[repr(C)]
struct Inner<I, T> {
info: I,
data: [T; 0],
}
impl<I: PrefixedArrayInfo, T> PrefixedArray<I, T> {
pub fn allocate(info: I) -> Self {
assert_ne!(0, ::std::mem::size_of::<T>(), "ZST not supported");
let mut data = Vec::<I>::with_capacity(Self::vec_cap(info.capacity()));
let inner = data.as_mut_ptr();
unsafe {
ptr::write(&mut *inner, info);
}
mem::forget(data);
PrefixedArray { inner: inner as _ }
}
fn vec_cap(len: usize) -> usize {
let bytes = mem::size_of::<I>() + mem::size_of::<T>() * len;
div_round_up(bytes, mem::size_of::<I>())
}
#[inline]
pub unsafe fn write(&mut self, offset: usize, value: T) {
ptr::write(self.data_mut().offset(offset as isize), value);
}
#[inline]
pub fn as_slice(&self) -> &[T] {
unsafe { slice::from_raw_parts(self.data(), self.len()) }
}
#[inline]
pub fn as_mut_slice(&mut self) -> &mut [T] {
unsafe { slice::from_raw_parts_mut(self.data_mut(), self.len()) }
}
#[inline]
pub unsafe fn clone_shallow(&self) -> Self {
PrefixedArray { inner: self.inner }
}
#[inline]
pub unsafe fn drop_and_deallocate(&mut self) {
let cap = self.info().capacity();
ptr::drop_in_place(self.as_mut_slice());
ptr::drop_in_place(&mut *self);
Vec::from_raw_parts(self.inner, 0, Self::vec_cap(cap));
}
pub fn info(&self) -> &I {
&self.inner().info
}
pub fn info_mut(&mut self) -> &mut I {
&mut self.inner_mut().info
}
fn data(&self) -> *const T {
self.inner().data.as_ptr()
}
fn data_mut(&mut self) -> *mut T {
self.inner_mut().data.as_mut_ptr()
}
fn len(&self) -> usize {
self.info().len()
}
fn inner(&self) -> &Inner<I, T> {
unsafe { &*self.inner }
}
fn inner_mut(&mut self) -> &mut Inner<I, T> {
unsafe { &mut *self.inner }
}
}
#[inline]
fn div_round_up(divident: usize, divisor: usize) -> usize {
1 + ((divident - 1) / divisor)
}
#[cfg(test)]
mod tests {
use super::{PrefixedArray, PrefixedArrayInfo, div_round_up};
use testdrop::{self, TestDrop};
#[test]
fn test_div_round_up() {
assert_eq!(6, div_round_up(6, 1));
assert_eq!(7, div_round_up(7, 1));
assert_eq!(8, div_round_up(8, 1));
assert_eq!(3, div_round_up(6, 2));
assert_eq!(4, div_round_up(7, 2));
assert_eq!(4, div_round_up(8, 2));
assert_eq!(2, div_round_up(6, 3));
assert_eq!(3, div_round_up(7, 3));
assert_eq!(3, div_round_up(8, 3));
assert_eq!(3, div_round_up(9, 3));
assert_eq!(4, div_round_up(10, 3));
}
struct Info {
len: usize,
cap: usize,
}
impl PrefixedArrayInfo for Info {
fn len(&self) -> usize {
self.len
}
fn capacity(&self) -> usize {
self.cap
}
}
#[test]
fn drop_and_deallocate() {
let test = TestDrop::new();
let v = &mut PrefixedArray::allocate(Info { len: 0, cap: 5 });
let (a, item_a) = test.new_item();
let (b, item_b) = test.new_item();
let (c, item_c) = test.new_item();
let (d, item_d) = test.new_item();
let (e, item_e) = test.new_item();
fn test_write<'a>(
v: &mut PrefixedArray<Info, testdrop::Item<'a>>,
id: usize,
item: testdrop::Item<'a>,
index: usize,
) {
unsafe {
let len = v.inner().info.len;
v.write(len, item);
v.inner_mut().info.len = len + 1;
}
assert_eq!(index + 1, v.len());
assert_eq!(index + 1, v.as_slice().len());
assert_eq!(index + 1, v.as_mut_slice().len());
assert_eq!(id, v.as_slice()[index].id());
assert_eq!(id, v.as_mut_slice()[index].id());
}
test_write(v, a, item_a, 0);
test_write(v, b, item_b, 1);
test_write(v, c, item_c, 2);
test_write(v, d, item_d, 3);
test_write(v, e, item_e, 4);
v.inner_mut().info.len = 3;
unsafe {
v.drop_and_deallocate();
}
test.assert_drop(a);
test.assert_drop(b);
test.assert_drop(c);
test.assert_no_drop(d);
test.assert_no_drop(e);
}
}